1. Field of the Invention
The present invention relates to a cable-type steering device in which a steering wheel is connected with a steering gearbox with cables, such as Bowden cables, and more particularly, to a steering torque-detecting device for the cable-type steering device.
2. Description of the Prior Art
A cable-type steering device is proposed in which a flexible transmission means, such as a Bowden cable, replaces a steering shaft for connecting a steering wheel with a steering gearbox (for example, as shown in Japanese Patent Unexamined Publication No. Hei. 8-2431). Adopting such a cable-type steering device enables not only the free selection of a position for the steering wheel relative to the position of the steering gearbox but also the transmission of less vibrations of the steering gearbox to the steering wheel.
In a case where a power steering device is combined with a cable-type steering device, such as described above, it is necessary to detect a steering torque that is to be inputted into a steering wheel in order to control the operation of an assist motor. In a conventional steering torque-detecting device, a potentiometer is disposed between a pair of cables extending from a driving pulley, and rollers provided at ends of a V-shaped detecting arm fixed to a detecting shaft of the potentiometer are adapted to be brought into elastically springing abutment with the pair of cables, respectively. When a steering torque applied to the steering wheel rotates the driving pulley, the tension of one of the pair of cables increases, while that of the other decreases, and this rotates, together with the detecting shaft, the detecting arm, the roller of which is pressed against the cable, the tension of which increases, whereby the output from the potentiometer is changed, a steering torque being thereby detected.
With the conventional steering torque-detecting device described above, however, since there are provided therein a number of components and moving portions, the construction of the device becomes complicated, resulting in a drawback that it is difficult to secure sufficient durability. In addition, since the detecting arm generates micro-vibrations when an inner cable made of a stranded metal wire comprising a metallic strand moves along the roller while rotating it, micro-vibrations so-generated are then transmitted to the detecting shaft of the potentiometer leading to a drawback that the detection accuracy of the potentiometer is deteriorated. Moreover, since the inner cable is bent in a substantially V-shape at a portion where it abuts with the roller in response to the fluctuation in tension of the cable itself, there is also provided a drawback that the rigid feeling of the steering wheel is lowered, whereby the steering feeling is deteriorated.